Nervous System: Definition, Parts, Functions, Types

Nervous System: Have you ever wondered how a swimmer or hurdler regulates their arm and leg motions with flawless synchronisation and accuracy? It is caused in humans by the interaction of complex systems. For such regulation and synchronisation, the neurological and endocrine systems collaborate. The neurological system communicates by nerve impulses, whereas the endocrine system communicates via chemical messages from hormones. In this post, we’ll go through the nervous system in further detail, including its functions, components, and so on.

What is the Nervous System?

We can do things in which we have to think and also in which we don’t have to. Like our heartbeats, we breathe without thinking. We can read, write, walk, cycle, etc. with our knowledge. As soon as we put food in our mouth, our salivary glands start secreting saliva. How are these possible? These are possible because the nervous system passes information from one part of the body to another.

Nervous System Definition

The human nervous system is the system that receives information from the surroundings, processes it and responds accordingly.

Unit of Nervous System: Neuron

1. The neuron is the structural and functional unit of the nervous system, i.e. all the parts of the nervous system like the brain, spinal cord are made of neurons.
2. The neuron is the largest cell in the body.

3. It consists of:-

a. Cell body or Soma or Cyton has a prominent nucleus, cytoplasm, Nissl’s granules, and no centrosomes.

b. Dendrites are thread-like structures that are cytoplasmic extensions of the cell body.

c. Axon is a long fibre-like cytoplasmic process arising from a conical projection called axon hillock, of the cyton

d. The plasma membrane of an axon is called axolemma and its cytoplasm is called axoplasm.

4. The dendrites pick up sensations from the finest part of the body and transmit the same to the cell body.

5. Axon is branched terminally. And the terminal branches are called telocentric.

6. Axon terminals are often swollen knob-like and contain neurotransmitters.

7. Axon terminals are close to the dendrites of other neurons but are not connected, rather separated by a gap called synaptic clefts or synapses.

8. Myelin sheath, a white insulating sheath, covers the axon of most of the neurons. It is not continuous and forms gaps or the nodes of ranvier.

Interesting Facts

Do you know that our neurons have lost the capability to divide.

Once fully formed, they never divide and remain in the G₀ phase of interphase throughout the life.

Types of Neuron

1. Sensory neuron – This type of neuron carries messages from the receptors to the brain or spinal cord.
2. Motor neuron – This type of neuron carries messages from the brain to the effector organs.
3. Association neuron – This type of neuron connects sensory and

Transmission of Nerve Impulses

1. Transmission of the information in the nervous system is in the form of action potentials from one region to another along the axon is called nerve impulse.

2. Nerve impulses are transmitted through this synaptic cleft via neurotransmitters e.g., acetylcholine, adrenaline (epinephrine), glutamic acid, etc. which are released by the synaptic knob of the axon terminal.

a. Nerve impulses are transmitted to the next neuron, an organ, muscle, or gland.

b. Transmission of nerve impulse takes place through the following path:-

3. The transmission of nerve impulses takes place from one neuron to another through gaps called synapses through neurotransmitters which are the chemicals secreted by the axon terminal.

4. The axon terminal expands to form a presynaptic knob and the membrane of dendrites expands to form the postsynaptic membrane. The presynaptic knob releases neurotransmitters which bind to the postsynaptic membrane.

5. As the neurotransmitter is released on one side of the synapse, the transmission of nerve impulses occurs only in one direction.

Functions of Nervous System

Following are the functions of the nervous system:-

1. To provide information on the internal and external environment of the body.
2. To control and coordinate the voluntary and involuntary activities of the body.
3. To assimilate the experiences such as memory, learning and intelligence.

Parts of the Nervous System

Broadly, the nervous system is divided into two parts, i.e.,

1. Central nervous system (CNS) and Peripheral nervous system (PNS).
2. PNS includes Somatic nervous system (voluntary) and Autonomic nervous system (involuntary).

Nervous System in Humans

Central Nervous System

CNS is divided into the brain and spinal cord.

Brain (Encephalon)

1. Brain is the highest coordinating centre in the body, present inside the cranium. An average human brain weighs about \({\rm{1}}{\rm{.5}}\,{\rm{kg}}{\rm{.}}\) The complete brain is made of \(100\) billion neurons.
2. Brain and spinal cord are protected by \(3\) protective layers called meninges:
   a. Dura mater is the tough outermost fibrous layer present just beneath the cranium and is the most protective one.
   b. Arachnoid is the middle layer present between dura and pia mater, that has a network of collagen fibers that looks like spider net.
   c. Pia mater is the innermost layer, vascular and made of squamous epithelium.

Cerebrospinal Fluid (CSF)

1. Between arachnoid and pia mater, there is subarachnoid space. This space is filled with Cerebrospinal Fluid (CSF), which is clear, colourless, alkaline fluid. This is found in the brain and spinal cord.
2. CSF is rich in nutrients, minerals, hormones, urea and respiratory gases.
   a. It acts like a cushion for the brain and protects it from injury and mechanical shocks.
   b. It supplies food and oxygen to different parts of the brain and spinal cord.
   c. It picks up wastes like carbon dioxide, urea, etc. from the CNS.

Parts of Brain

The brain is divided into forebrain, midbrain, and hindbrain. In the following chart subdivisions of the brain is given:-

1. Forebrain (Prosencephalon)- Forebrain includes cerebral hemispheres or cerebrum, olfactory lobes, and diencephalon (thalamus and hypothalamus).

a. Olfactory lobes are a paired structure that is present on the inferior surface of the cerebrum. This controls the sense of smell.

2. Cerebrum is the largest part of the brain which is divided into right and left hemispheres.

i. It is divided into two hemispheres which are connected by a tract of nerve fibres called the corpus callosum.

ii. The layer of cells which covers the cerebral hemisphere is called the cerebral cortex. The cerebral cortex has a number of folds, formed by elevations called gyri and depressions called sulci. This is to increase the surface area to accommodate more and more nerve cells.

iii. Cerebrum is divided into four lobes:-

–Frontal lobe for creative ideas, emotion, memory.

–Parietal lobe for the perception of touch, pain, heat, and cold.

–Temporal lobe for memory, smell, sound, and language development.

–Occipital lobe for vision.

3. Diencephalon- is a part of the cerebrum which lies on its inferior side. It consists of:

i. Thalamus- It relays pain and pressure to the cerebrum.

ii. Hypothalamus- It controls body temperature and pituitary gland

4. Midbrain (Mesencephalon) is located between the thalamus/hypothalamus and pons of the hindbrain.

a. It consists of fibrous tracts called cerebral peduncles which connect the hindbrain and forebrain and also has four swollen regions called corpora quadrigemina, which cause reflex movements of head and neck, sight, and hearing reflexes.

5. Hindbrain (Rhombencephalon) comprises of:

a. Cerebellum – It lies behind the cerebrum. It controls the voluntary muscular actions and helps in the maintenance of equilibrium, the posture of the body while bending, jumping, walking, etc.

b. Pons – It is the middle part of the brain stem. It connects the cerebellum, medulla oblongata, and cerebrum.

c. Medulla oblongata – It lies below the cerebellum and continues into the spinal cord. It regulates respiration, heartbeat, blood pressure, circulation, peristaltic movements, etc. It is the centre of swallowing, sneezing, vomiting, coughing, etc.

6. The brain stem consists of the medulla oblongata, pons, and midbrain.

Spinal Cord

The second part of the CNS is the spinal cord.

1. It is a narrow cylindrical, the lower part of the central nervous system which is \(43-45\) cms long, running till the early part of the lumbar region.
2. It is also protected by meninges and has inner grey and outer white matter and has CSF.
3. It provides attachment to \(31\) pairs of spinal nerves which connect it to tissues of the trunk, girdle and limbs.

Functions of Spinal Cord

1. It controls reflex actions.
2. It contains sensory and motor neurons which can transfer messages to and from the brain and effector organs.

Peripheral Nervous System (PNS)

PNS is divided into:

1. Somatic nervous system – It controls voluntary muscles and their actions.
2. Autonomic nervous system – It controls involuntary muscles and their actions.

The somatic nervous system includes all the nerves, i.e. cranial nerves (that arise from the brain) and spinal nerves (that arise from the spinal cord). There are \(12\) pairs of cranial nerves that are classified into 3 categories:-

1. Afferent/sensory nerves – It carries impulses from sense organs to CNS.
2. Efferent/Motor nerves – It carries nerve impulses from CNS to organs.
3. Mixed nerves – They function as sensory as well as motor nerves.

Spinal nerves are \(31\) pairs. Every spinal nerve is a mixed nerve having both sensory and motor fibres.

The autonomic nervous system includes paired nerves that are present on either side of the backbone. This system controls involuntary actions. It includes:-

1. Sympathetic nervous system– It includes nerves between the neck and waist. It works under stressful conditions and its working is controlled by adrenaline.
2. Parasympathetic nervous system– It includes nerves above the neck and below the sacral. It works under normal conditions and its working is controlled by acetylcholine.

Parasympathetic and sympathetic works opposite to each other.

Summary

We learned about our nervous system from the article. This system is made up of two parts: the central nervous system and the peripheral nervous system. The nervous system absorbs information from its environment, analyses and interprets it, and then responds. The nervous system also transmits data from one internal system to another. It also governs and coordinates the body’s voluntary and involuntary processes.

FAQs on Nervous System

The frequently asked questions on the Nervous System are given below:

Q.1. What is the nervous system and its types?
Ans: The human nervous system is the system that receives information from the surroundings, processes it, and responds accordingly. It comprises of:-
a. Central nervous system
b. Peripheral nervous system 

Q.2. What are the 4 main functions of the nervous system?
Ans: Main functions of the nervous system are:-
a. It provides information of the internal and external environment of the body.
b. It control and coordinate the voluntary activities of the body
c. It assimilates the experiences such as memory, learning, and intelligence.
d. Controls involuntary actions, reflex actions.

Q.3. What are the symptoms of a weak nervous system?
Ans: Symptoms of a weak nervous system are:-
a. Sudden headache
b. Loss of feeling of tingling
c. Unable to pick up any object
d. Loss of memory
e. Seizures
f. Slurred speech 

Q.4. What are the 3 parts of the nervous system?
Ans: Nervous system comprises the central nervous system (Brain, Spinal cord) and peripheral nervous system.

Q.5. What are the 5 main parts of the nervous system?
Ans: Nervous system is divided into-
a. Central nervous system– It is divided into the brain and spinal cord.
b. Peripheral nervous system– It is divided into sympathetic and parasympathetic nervous systems.
c. Sense organs

Study About Neural Control and Coordination Here

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